The present invention relates to a looper for thick metal strip. More particularly this invention concerns such a looper used in a rolling operation for strip 4 mm to 25 mm thick and a method of looping such strip.
In many production operations it is essential that a metal strip be fed continuously in to some production machine at a slow but constant rate. The input of strip cannot be stopped, as for instance in a pipe-making operation that shapes the strip into a tube and welds its edges together.
Hence loopers are known, for instance from German 198 38 780, in which the strip passes in loops between a pair of horizontally spaced and movable carriages. When, for instance, a leading end of a fresh strip has to be welded to the trailing end of the strip in production, the two carriages are moved together to allow the strip movement to be stopped at the intake end for the welding operation while continuing to allow it to exit from the looper at a constant speed. Such systems only work well with relatively thin strip, not for the 4 mm to 25 mm thick stock used in many operations.
U.S. Pat. No. 5,865,393 of Kreft describes another system where the loop ends are spaced vertically and where the weight of the structure holding the upper loop ends is borne by the upward pull on the structure holding the lower loop ends. This system, mainly because of the small radius it forces the strip through at the loop ends, only works with thin strip.
EP 0,076,245 describes a system having a common frame holding coaxial roller baskets whose rollers extend parallel to the horizontal basket axis. S-loops are formed near the roller baskets. This is only possible with, once again, relatively flexible and thin metal strip.
It is therefore an object of the present invention to provide an improved looper for thick metal strip.
Another object is the provision of such an improved looper for thick metal strip which overcomes the above-given disadvantages, that is which can handle steel strip in the thickness range of 4 mm to 25 mm.
A further object is to provide and improved method of looping metal strip.
A looper for thick metal strip has according to the invention a large-diameter outer basket centered on an upright axis and a small-diameter inner basket axially above the outer basket and centered on an upright axis. The strip is fed on edge and generally tangentially into the outer basket to form therein a large-diameter spiral having an inner end. Then the strip is fed upward from the spiral inner end around the inner basket and is finally pulled tangentially from the inner basket. The strip is straightened generally as it leaves the inner basket.
Thus with the system of this invention the strip is actually stored in a spiral of such size that even relatively thick strip can easily be bent to fit to it. The spiral is large enough and its turns are loose enough that the speed with which the strip can be fed into the outer turn can be quite a bit different from that at which it is pulled from the inner turn. The somewhat tighter diameter that the strip must follow as it is pulled out of the spiral is relatively short so that it can be managed without great energy expenditure, and the straightener takes out any plastic deformation imparted to the strip as it moves around the inner basket.
According to the invention the straightener is mounted on the inner basket. In addition a guide conducts the strip from the inner spiral end up around the inner basket and to the straightener. This guide conducts the strip through less than 360xc2x0 about the inner-basket axis, normally about 270xc2x0. The guide includes a set of rollers including a furthest downstream roller inclined at 15xc2x0 to 25xc2x0 to the inner-basket axis.
The inner-basket axis is offset horizontally to the outer-basket axis. Thus the strip passes smoothly from the inner turn of the spiral up around the inner basket. In fact according to the invention an outer portion of the inner basket lies generally above the spiral inner end so that the strip passes helicoidally from the spiral inner end to the straightener.
As the strip is normally produced flat, that is with its thickness dimension and its width horizontal rollers are provided for twisting the strip from a flat position to an on-edge position both at the input and output end. Thus a typical system where the incoming strip is produced by rolling billets can work with a standard pipe-making machine.
The input feeder includes a pair of upright driven rollers pinching the strip and a hold-down roller bearing downward on the strip. This keeps the strip down in the spiral, normally riding on floor rollers.
The strip looping method according to the invention thus comprises the steps of feeding the strip horizontally on edge into a large-diameter outer basket centered on an upright axis and forming in the basket a large-diameter multiturn spiral having an inner end. Then the strip is guided from the inner end upward in a helicoid of less than 360xc2x0 around a small-diameter inner basket axially above the outer basket and centered on an upright axis. Finally the strip is pulled horizontally and tangentially from the inner basket above the spiral in the outer basket.